1. Field of the Invention
The present invention relates to an electronic device and, in particular, to an electronic device in integrated technology.
2. Description of Related Art
In order to form a device in integrated technology, a process step in which an etching process takes place is often performed when manufacturing a device. An etching process can, in general, be characterized by the fact that the surface of a solid body is eroded during this process using an etchant, wherein the etchant includes chemical reagents and/or particles having a high kinetic energy. The etching rate of an etchant is also depends on the material to be etched and on a possible dopant concentration of the solid body. Because an etchant has different etching rates regarding the material to be etched, a selectivity of the etchant forms regarding a material to be etched compared to another material. This material can, for example, have a masking or protecting function. In addition, the etching rate of an etchant can depend on the etching direction (anisotropic etching).
In principle, etching methods can be divided into chemical, chemical-physical and physical etching methods. While chemical, in particular wet-chemical, etching methods have a high selectivity regarding the medium to be etched and a high anisotropy regarding the crystal orientation, it can be noted that in these etching methods an irregular etching process takes place, for example by the formation of gas bubbles, and additionally under-etching occurs by a poorly directed etching behavior of the etchant in the material to be etched. For this reason, wet-chemical etching methods only have a low resolution ability, which is why the manufacture of devices having small dimensions is problematic with this etching method. Physical etching methods (such as, e.g., the sputter etching method or the ion beam etching method), in contrast possess considerably better dissolution qualities since, in these methods, the particles of the etching medium (such as, e.g., electrons or ions) are accelerated and impinge on the medium to be etched in a directed way. A high anisotropy of the etching process can be achieved by this, whereby a high dissolution ability can be realized, which proves to be of advantage for manufacturing devices having small dimensions. By virtue of the partly high kinetic energy of the particles of the etching medium, a lower selectivity of the etching medium regarding the material to be etched is, however, obtained in physical etching methods, compared to chemical etching methods since the etching effect basically results from knocking out components of the material to be etched. In particular, a non-selective etching behavior is of high disadvantage when areas of the device essential for a fault-free functionality of the device are damaged by the etching process. Damage resulting from a physical etching method employed in insulation or dielectric layers which are arranged below the material to be removed by the etching can be mentioned as an example. In particular damage by thinning the insulation or dielectric layers mentioned can be observed. Since the insulation or dielectric layer mentioned considerably determines the behavior of a device to be formed (in particular of a capacitive device), attention must be paid to not damaging such layers when manufacturing the device.
In order to achieve a high dissolution and, at the same time, a high selectivity when manufacturing a device having small dimensions, a plasma etching method is often employed. Gasses activated by plasma and reactive gasses are used for the etching process. The activation of the gasses thus mostly takes place by thermal and high-frequency electromagnetic excitation. The plasma etching method thus represents a chemical-physical etching method which basically combines the advantages of a purely chemical etching method and the advantages of a purely physical etching method.
The plasma etching method does, however, also have some disadvantages apart from the advantages. It is to be mentioned here in particular that kinetic energy is supplied to the particles of the etching medium by thermal or high-frequency electromagnetic excitation of the etching medium, but the formation of a preferred direction of movement (i.e. the formation of a directivity) often does not take place. Effects exemplarily illustrated in FIG. 8 are caused by this.
Firstly, FIG. 8 shows a substrate 800 comprising an upper layer 802 which, for example, includes an insulating or dielectric material. A starting layer 806 which, for example, includes a conductive material, is deposited on the surface 804 of the upper layer 802. In order to form a device, a covering layer 810 is deposited on the surface 808 of the starting layer 806 and patterned in such a way that the area of the starting layer 806 to be removed is exposed. By a subsequent etching process, in particular a plasma etching process, the areas of the starting layer 806 exposed by the patterned covering layer 810 are removed so that the result is a useful structure 814. When an upper electrode of a metal isolator metal capacity (MIMCAP) is, for example, formed by the useful structure 814 in combination with the insulating upper layer 802 and the (preferably conductive) substrate 800, the etching medium used in the etching process should, in the ideal case, be highly selective regarding the material of the upper layer 802. This means that the upper layer 802 (such as, e.g., an insulating layer or a dielectric) should not be damaged at the etching edge 816 of the useful structure 814 since an undesired electric behavior results otherwise.
In practice, it shows, however, that the upper layer 802, i.e. the insulation layer or the dielectric, is damaged by applying a plasma etching method for forming the useful structure 814. In addition, the side edges 818 of the useful structure (such as, e.g., the side edges of the upper electrode of an MIMCAP) are under-etched by the plasma etching method, as in shown in FIG. 8. Inhomogeneities of the electric field between the useful structure 814 and the substrate 800 are caused by this, in particular at the etching edges 816 of the useful structure 814, as is exemplarily shown in FIG. 8 with the help of the field lines 820 of the electric field illustrated.
Basically, the damage of the upper layer 802 and the under-etching of the etching edge 816 result from an isotropic etching caused by a lacking directivity of the particles 822 of the etching medium perpendicularly to the upper layer 802.
Furthermore, margin structures, i.e. useful structures at the margins of a field of several useful structures (such as, e.g., of an MIMCAP field) are affected more strongly than useful structures within the useful structure field. Such a case is illustrated in FIG. 9 in which a margin structure 900 is arranged at the margin of a field of several useful structures 902 within the field. In particular, it can be seen that the useful structure side edges 904 and the etching edges 906 lying within the field of the useful structures 902 are not damaged to such an extent by the isotropic plasma etching as the useful structure side edges 818 and etching edges 816 arranged at the margin regions.
Apart from the lacking directivity of the particles 822 of the etching medium mentioned above, such an effect results from the differing saturation behavior of the etching medium while etching useful structure side edges 902 within a useful structure field compared to etching useful structure side edges 818 at the outer margin of the useful structure field. In particular due to the fact that a useful structure side edge 904 opposite to the useful structure side edge 904 is formed at the same time within a useful structure field while etching a useful structure side edge 904, a saturation effect of the reactivity of the particles 822 of the etching medium occurs since in such a case firstly a considerably larger surface is to be etched with basically the same amount of etching medium in the environment of the useful structure side edge 904 to be etched, compared to a useful structure side edge 818 arranged at the margin region of a useful structure field, and secondly a geometrical arrangement is to be realized by forming a gap between the two opposing useful structure side edges 904 within a useful structure field, the arrangement having less favorable features for a fast diffusion of the particles 822 of the etching medium consumed by the etching process away from the material to be etched, than is the case for outer useful structure side edges 818 at the margin region of a useful structure field. By such an etching process, useful structure side edges 904 can be generated within a useful structure field, which, compared to outer useful structure side edges 818 of a margin structure 900, have considerably less under-etching of the etching edges and a considerably smaller damage of the upper layer 802.
It has proved to be of particular disadvantage that, by damaging the upper layer 802 (such as, e.g., the insulation layer or the dielectric), the etching attack, the lifetime and the dielectric strength of the devices formed, compared to undamaged devices, are reduced, which results in an increase of the defect density and of the early failure rate. In addition, the electrical behavior of the margin structure 900 is impeded by damaging the upper layer 802 and under-etching the etching edge 816, respectively, which results in a sometimes considerable deviation of the device value from the expected device value.